1. Field of the Invention
The invention relates to a coating solution for a glucose sensing membrane and a method of manufacturing an optical glucose sensor chip.
2. Description of the Related Art
As disclosed in Jpn. Pat. Appln. KOKAI Publication No. 9-61346, an optical glucose sensor chip has a structure including a glass substrate, a pair of gratings formed in the main face of the substrate for receiving and sending light to the substrate, and a glucose sensing membrane having a molecule recognition function and an information conversion function formed on the main face of the substrate between the gratings. The glucose sensing membrane is formed by applying a coating solution for a glucose sensing membrane containing an oxidizing enzyme or a reducing enzyme of glucose, a reagent for generating a substance to be reacted with a coloring agent, a coloring agent, and a membrane-forming polymer compound to an optical waveguide path layer and drying the solution.
The coating solution for a glucose sensing membrane of the glucose sensor chip is conventionally produced by the following first to ninth steps.
The first step: producing an isopropyl alcohol solution containing a coloring agent (e.g. tetramethylbenzidine) in a desired concentration.
The second step: adding isopropyl alcohol to the solution.
The third step: producing a mixed solution by adding pure water to the diluted isopropyl alcohol solution.
The fourth step: adding a buffer agent (e.g. a phosphoric acid buffer) to the mixed solution.
The fifth step: adding an aqueous solution of a reagent (e.g. a peroxidase) generating a substance to be reacted with the coloring agent to the solution obtained in the fourth step.
The sixth step: adding an aqueous solution of a glucose oxidizing enzyme (e.g. a glucose oxidase) to the solution obtained in the fourth step.
The seventh step: shaking the solution obtained in the sixth step up side down.
The eighth step: producing a mixed solution by adding an aqueous solution of a membrane-forming polymer compound (e.g. carboxymethyl cellulose) to the solution shaken up side down.
The ninth step: sufficiently stirring the mixed solution.
However, the conventional method of producing the coating solution for a glucose sensing membrane required a large number of steps and these steps are carried out every time to produce the glucose sensor chip. Therefore, there occurs a problem that the functions may become uneven among production lots.
Because of that, it has been tried to previously produce a large quantity of the coating solution for a glucose sensing membrane so as to avoid dispersion of the functions among production lots. However, the coating solution for a glucose sensing membrane produced in a large quantity has a problem that the activities of the glucose oxidizing enzyme (e.g. glucose oxidase) and the reagent (e.g. peroxidase) generating a substance to be reacted with the coloring agent, which are the components of the coating solution, are decreased during the storage of the coating solution.